The invention relates to a reaction arrangement on a hydraulic servo-valve arrangement which is designed in a manner of a rotary-slide arrangement and has a rotary slide and a control bush coaxially surrounding the latter and rotatable relative to the rotary slide and which is provided, in particular, for power steering systems of motor vehicles.
Hydraulic power steering systems are installed as standard in most motor vehicles. It is basically known, here, for the manual force detectable on the steering wheel or to be applied during steering maneuvers to be modified as a function of parameters, in order, for example, to make the steering somewhat heavier at high speed and especially light at low speed, in particular within a speed range typical of a parking manoeuvre. For this purpose, so-called reaction arrangements are used, by means of which the force necessary for adjusting the servo-valve arrangement can be modified. As regards a servo-valve arrangement designed in the manner of a rotary-slide arrangement, this is tantamount to the fact that the force necessary for rotating the rotary slide and control bush relative to one another can be modified in a controllable way.
In this respect, it has already been proposed, according to DE 196 16 439 A1 (not previously published), to arrange axial grooves, with flanks spreading radially outwards in a V-shaped manner, on a shaft part located on the rotary-slide side and connected fixedly in terms of rotation to the rotary slide and to arrange radial guides for reaction bodies, capable of being pressed into the axial grooves, on a bush portion which coaxially surrounds the abovementioned shaft part and is connected fixedly in terms of rotation to the control bush, the reaction bodies then being capable of being subjected to hydraulic pressure controllable as a function of parameters, so that the said reaction bodies seek to penetrate with controllable force into the axial grooves and consequently oppose to relative rotation between the shaft part and bush portion a controllable resistance which also depends on the shape of the reaction bodies, for example balls, and on the steepness of the flanks of the axial grooves.
In a power steering system known from DE 42 34 571 A1, a centring device, which has a torsion bar clamped between an input shaft and an output shaft, is provided for the servovalve. Since the torsion bar does not allow exact mid-centring between the rotary slide and a valve bush, a spring element is provided, which is connected by means of weld spots to a ring fixed in the rotary slide, is provided, the said spring element being designed as a corrugated spring. The spring element carries a centring piece which is provided with pairs of oblique faces and which is pressed under prestress against rolling bodies. The rolling bodies are supported in corresponding pairs of oblique faces of a further centring piece which is connected to the drive shaft via a connecting part for the torsion bar. When the input shaft and output shaft are rotated relative to one another, the cooperation of the rolling bodies with the abovementioned oblique faces of the centring pieces causes an axial force to be generated which is converted into a resetting force and ensures that the valve is set exactly into its middle position.
DE 43 29 999 C1 relates to a servovalve having an axially displaceable control sleeve. Here, the valve consists of an input shaft, an output shaft, a torsion bar, which is connected at one end to the input shaft and at the other end to the output shaft, a valve sleeve surrounding the input shaft and a control sleeve arranged between the valve sleeve and the input shaft and axially displaceable as a function of a rotation of the input shaft, control grooves arranged in the valve sleeve and on the axially displaceable control sleeve cooperating hydraulically. These control grooves are arranged in such a way that the hydraulic flow is interrupted when the servovalve is in the middle position. By means of an actuating element arranged on the servovalve, a force counteracting the axial displacement is exerted on the control sleeve when the force resulting from the pressure acting on the actuator reaches a predetermined ratio to the force acting on the input shaft.
The object of the invention, then, is to indicate an advantageous design for a reaction arrangement of the type specified in the introduction.
This object is achieved in that, in addition to the above-described shaft part and the associated bush part, there is provided a housing surrounding the bush part and having at least one radial orifice, through which the reaction bodies can be inserted into the radial bores of the bush part when the latter is appropriately positioned, the housing and the bush part being capable of being axially adjustable relative to one another between a mounting position, in which the housing-side radial orifice and the radial bores of the bush part lie in a common radial plane with respect to the bush axis, and an operating position, in which the radial orifice is axially offset relative to the radial bores and the reaction bodies cannot in any way be pushed in a bolt-like manner into the radial orifice.
The invention is based on the general idea of arranging the reaction bodies in the housing only after the shaft part located on the rotary-slide side and the bush part located on the control-bush side have been mounted, the said housing then being capable of surrounding the reaction bodies in a cage-like manner.
This at the same time affords the advantage that the shaft part with the axial grooves may have a larger diameter, in particular a diameter which is large in comparison with the rotary slide, and the torque capable of being generated is correspondingly high.
The radial orifice may, if appropriate, perform a double function, by serving, on the one hand, for inserting the reaction bodies and, on the other hand, as a hydraulic connecting orifice, via which the reaction bodies are subjected, for reaction control, to the hydraulic pressure controllable as a function of parameters.
Moreover, as regards preferred features of the invention, reference is made to the claims and to the following explanation of the drawing, by means of which particularly preferred embodiments of the invention are described.